Halogenated aromatic hydrocarbons such as chlorinated or brominated dibenzo-p-dioxins, dibenzofurans or biophenyls are extremely toxic environmental pollutants produced inadvertently in industrial processes and/or combustion. These compounds exert their biochemical effects such as induction of cytochrome P-450c and d, as well their toxicological effects, such as chloracne and thymic atrophy, via the the dioxin receptor, an intracellular, soluble receptor protein with high affinity for 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD). We will continue our efforts to investigate the molecular mechanism of dioxin toxicity by characterization, purification, and cloning of the dioxin receptor. We have recently shown that the dioxin receptor represents a dioxin-inducible DNA-binding factor, notably similar to the glucocorticoid receptor. There are many other mechanistic, biochemical and functional analogies, which indicate a possible relatedness between the dioxin receptor and the gene family of steroid hormone receptors. Given our strong background in steroid receptor biochemistry, we therefore propose to combine structural studies on the dioxin receptor represents a previously unidentified member of the gene family of receptors for steroid hormones, thyroid hormones and retinoic acid. More specifically, we propose to purify the receptor further from cytosol and/or nuclei and to isolate ad clone the TCDD receptor cDNA and gene, to investigate which properties of TCDD receptor ligands that, in addition to steric factors, are important determinants for their receptor binding, and to study TCDD receptor-DNA interaction in order to define the specificity of DNA- binding of the TCDD receptor. Furthermore, we propose to develop monoclonal antibodies to the TCDD receptor, to investigate the mechanism of TCDd receptor activation by means of studies of its interaction with the glucocorticoid receptor-associated Mr 90,000 heat shock protein, to analyze the primary structure of the TCDD receptor and to express this protein in pro- and/or eukaryotic expression systems.